let callbacks = []

function loadedTinymce() {
	// to fixed https://github.com/PanJiaChen/vue-element-admin/issues/2144
	// check is successfully downloaded script
	return window.tinymce
}

const dynamicLoadScript = (src, callback) => {
	const existingScript = document.getElementById(src)
	const cb = callback || function() {}

	if (!existingScript) {
		const script = document.createElement('script')
		script.src = src // src url for the third-party library being loaded.
		script.id = src
		document.body.appendChild(script)
		callbacks.push(cb)
		const onEnd = 'onload' in script ? stdOnEnd : ieOnEnd
		onEnd(script)
	}

	if (existingScript && cb) {
		if (loadedTinymce()) {
			cb(null, existingScript)
		} else {
			callbacks.push(cb)
		}
	}

	function stdOnEnd(script) {
		script.onload = function() {
			// this.onload = null here is necessary
			// because even IE9 works not like others
			this.onerror = this.onload = null
			for (const cb of callbacks) {
				cb(null, script)
			}
			callbacks = null
		}
		script.onerror = function() {
			this.onerror = this.onload = null
			cb(new Error('Failed to load ' + src), script)
		}
	}

	function ieOnEnd(script) {
		script.onreadystatechange = function() {
			if (this.readyState !== 'complete' && this.readyState !== 'loaded') return
			this.onreadystatechange = null
			for (const cb of callbacks) {
				cb(null, script) // there is no way to catch loading errors in IE8
			}
			callbacks = null
		}
	}
}

export default dynamicLoadScript
